1. Field of the Invention
The present embodiments relate generally to laser systems and more particularly to laser systems and methods used for seam welding.
2. Description of the Prior Art
High-powered laser sources are reliable and effective tools for both low and high-power industrial applications. For example, high-power laser sources are used in many applications for material processing, like annealing, welding, and soldering. Most of the available products generate an output which approximates the fundamental, or TEM00, laser beam, having a Gaussian beam profile. TEM00 beams are generally spherical and the intensity peaks at the center of the beam and tails off rapidly toward the edges.
One of the biggest issues in welding is the unavoidable occurrence of gaps between the welding partners. Because of the gaps between the welding partners, Gaussian beam lasers are narrow and inefficient. For example, when a Gaussian beam is used to weld a butt joint between the two welding partners, the intensity around the middle axis of the beam is lost because there is no material to vaporize or to melt. As a result, lasers having non-Gaussian beam profiles have been used.
TEM01 laser beams, also called a doughnut beam because of their characteristic shape, produce a beam wherein the highest intensity is circularly distributed around the outside of the beam's width. While the doughnut beam has a wide seam, in welding applications, the doughnut beam is inefficient and produces undesirable results because the beam's power is not uniform across the weld gap and thus produces undesirable results.
Multi-mode laser beams, also referred to as a top-hat spread beam, produce a beam wherein the highest intensity is circularly distributed across a substantial portion of the beam's width. While the top-hat beam has a wide seam and produces a mostly-uniform beam, the beam is circular and the power density decreases quadratically with distance from the weld-gap. As a result, welding processes must be designed based on minimum energy needed at the edge of weld width to avoid causing thermal damage. Further, the top hat beam produces excess power in the center of the weld and the power outside of the weld zone generally causes distortion which, in turn, requires extra mass or compensating processing steps.
Carbon dioxide (CO2) lasers can produce an elliptical beam profile that may be used in welding applications, however, in such processes there is poor absorption by the welding partners as an amount of radiation is absorbed by the plasma generated from the weld surface. In order to suppress the plasma, CO2 lasers consume Helium, which is becoming increasingly expensive in the marketplace. CO2 lasers also have poor wall-plug efficiency.
Occasionally, it is desirable to weld two dissimilar metals. A successful weld between dissimilar metals is one that is as strong as the weaker of the two metals being joined, i.e., possessing sufficient tensile strength and ductility so that the joint will not fail in the weld. However, metals having dissimilar characteristics such as a different thickness, melting point, thermal conduciveness, or thermal expansion coefficient can create problems. The chance for problems grows when more of these conditions are present at the same time. If not performed properly and with great care, one metal may be over heated and the weld may become overly diluted or enriched in a certain component. As a result, cracking can occur when the metals form a weak or brittle alloy in the fusion zone. Currently, methods involving overlays, coatings, and filler materials are used to overcome some of the problems created when welding dissimilar methods. A need therefore exists for a welding technique wherein dissimilar metals can be joined successfully without the need of an overlay, coating, or filler material.
Each of these systems may also suffer from optimal efficiency, power, and brightness. Further, none of these systems produce a rectangular beam having a substantially uniform intensity profile across a weld gap.
The following application seeks to solve the needs and problems stated.